// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This file declares a HttpTransactionFactory implementation that can be
// layered on top of another HttpTransactionFactory to add HTTP caching.  The
// caching logic follows RFC 7234 (any exceptions are called out in the code).
//
// The HttpCache takes a disk_cache::Backend as a parameter, and uses that for
// the cache storage.
//
// See HttpTransactionFactory and HttpTransaction for more details.

#ifndef NET_HTTP_HTTP_CACHE_H_
#define NET_HTTP_HTTP_CACHE_H_

#include <list>
#include <memory>
#include <set>
#include <string>
#include <unordered_map>

#include "base/files/file_path.h"
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/non_thread_safe.h"
#include "base/time/clock.h"
#include "base/time/time.h"
#include "net/base/cache_type.h"
#include "net/base/completion_callback.h"
#include "net/base/load_states.h"
#include "net/base/net_export.h"
#include "net/base/request_priority.h"
#include "net/http/http_network_session.h"
#include "net/http/http_transaction_factory.h"

class GURL;

namespace base {
class SingleThreadTaskRunner;
} // namespace base

namespace disk_cache {
class Backend;
class Entry;
} // namespace disk_cache

namespace net {

class CertVerifier;
class ChannelIDService;
class HostResolver;
class HttpAuthHandlerFactory;
class HttpNetworkSession;
class HttpResponseInfo;
class HttpServerProperties;
class IOBuffer;
class NetLog;
class NetworkDelegate;
class ProxyService;
class SSLConfigService;
class TransportSecurityState;
class ViewCacheHelper;
struct HttpRequestInfo;

class NET_EXPORT HttpCache : public HttpTransactionFactory,
                             NON_EXPORTED_BASE(public base::NonThreadSafe) {
public:
    // The cache mode of operation.
    enum Mode {
        // Normal mode just behaves like a standard web cache.
        NORMAL = 0,
        // Disables reads and writes from the cache.
        // Equivalent to setting LOAD_DISABLE_CACHE on every request.
        DISABLE
    };

    // A BackendFactory creates a backend object to be used by the HttpCache.
    class NET_EXPORT BackendFactory {
    public:
        virtual ~BackendFactory() { }

        // The actual method to build the backend. Returns a net error code. If
        // ERR_IO_PENDING is returned, the |callback| will be notified when the
        // operation completes, and |backend| must remain valid until the
        // notification arrives.
        // The implementation must not access the factory object after invoking the
        // |callback| because the object can be deleted from within the callback.
        virtual int CreateBackend(NetLog* net_log,
            std::unique_ptr<disk_cache::Backend>* backend,
            const CompletionCallback& callback)
            = 0;
    };

    // A default backend factory for the common use cases.
    class NET_EXPORT DefaultBackend : public BackendFactory {
    public:
        // |path| is the destination for any files used by the backend, and
        // |thread| is the thread where disk operations should take place. If
        // |max_bytes| is  zero, a default value will be calculated automatically.
        DefaultBackend(CacheType type,
            BackendType backend_type,
            const base::FilePath& path,
            int max_bytes,
            const scoped_refptr<base::SingleThreadTaskRunner>& thread);
        ~DefaultBackend() override;

        // Returns a factory for an in-memory cache.
        static std::unique_ptr<BackendFactory> InMemory(int max_bytes);

        // BackendFactory implementation.
        int CreateBackend(NetLog* net_log,
            std::unique_ptr<disk_cache::Backend>* backend,
            const CompletionCallback& callback) override;

    private:
        CacheType type_;
        BackendType backend_type_;
        const base::FilePath path_;
        int max_bytes_;
        scoped_refptr<base::SingleThreadTaskRunner> thread_;
    };

    // The number of minutes after a resource is prefetched that it can be used
    // again without validation.
    static const int kPrefetchReuseMins = 5;

    // The disk cache is initialized lazily (by CreateTransaction) in this case.
    // Provide an existing HttpNetworkSession, the cache can construct a
    // network layer with a shared HttpNetworkSession in order for multiple
    // network layers to share information (e.g. authentication data). The
    // HttpCache takes ownership of the |backend_factory|.
    //
    // The HttpCache must be destroyed before the HttpNetworkSession.
    //
    // If |set_up_quic_server_info| is true, configures the cache to track
    // information about servers supporting QUIC.
    HttpCache(HttpNetworkSession* session,
        std::unique_ptr<BackendFactory> backend_factory,
        bool set_up_quic_server_info);

    // Initialize the cache from its component parts. |network_layer| and
    // |backend_factory| will be destroyed when the HttpCache is.
    HttpCache(std::unique_ptr<HttpTransactionFactory> network_layer,
        std::unique_ptr<BackendFactory> backend_factory,
        bool set_up_quic_server_info);

    ~HttpCache() override;

    HttpTransactionFactory* network_layer() { return network_layer_.get(); }

    // Retrieves the cache backend for this HttpCache instance. If the backend
    // is not initialized yet, this method will initialize it. The return value is
    // a network error code, and it could be ERR_IO_PENDING, in which case the
    // |callback| will be notified when the operation completes. The pointer that
    // receives the |backend| must remain valid until the operation completes.
    int GetBackend(disk_cache::Backend** backend,
        const CompletionCallback& callback);

    // Returns the current backend (can be NULL).
    disk_cache::Backend* GetCurrentBackend() const;

    // Given a header data blob, convert it to a response info object.
    static bool ParseResponseInfo(const char* data, int len,
        HttpResponseInfo* response_info,
        bool* response_truncated);

    // Writes |buf_len| bytes of metadata stored in |buf| to the cache entry
    // referenced by |url|, as long as the entry's |expected_response_time| has
    // not changed. This method returns without blocking, and the operation will
    // be performed asynchronously without any completion notification.
    // Takes ownership of |buf|.
    void WriteMetadata(const GURL& url,
        RequestPriority priority,
        base::Time expected_response_time,
        IOBuffer* buf,
        int buf_len);

    // Get/Set the cache's mode.
    void set_mode(Mode value) { mode_ = value; }
    Mode mode() { return mode_; }

    // Get/Set the cache's clock. These are public only for testing.
    void SetClockForTesting(std::unique_ptr<base::Clock> clock)
    {
        clock_.reset(clock.release());
    }
    base::Clock* clock() const { return clock_.get(); }

    // Close currently active sockets so that fresh page loads will not use any
    // recycled connections.  For sockets currently in use, they may not close
    // immediately, but they will not be reusable. This is for debugging.
    void CloseAllConnections();

    // Close all idle connections. Will close all sockets not in active use.
    void CloseIdleConnections();

    // Called whenever an external cache in the system reuses the resource
    // referred to by |url| and |http_method|.
    void OnExternalCacheHit(const GURL& url, const std::string& http_method);

    // Causes all transactions created after this point to effectively bypass
    // the cache lock whenever there is lock contention.
    void BypassLockForTest()
    {
        bypass_lock_for_test_ = true;
    }

    // Causes all transactions created after this point to generate a failure
    // when attempting to conditionalize a network request.
    void FailConditionalizationForTest()
    {
        fail_conditionalization_for_test_ = true;
    }

    // HttpTransactionFactory implementation:
    int CreateTransaction(RequestPriority priority,
        std::unique_ptr<HttpTransaction>* trans) override;
    HttpCache* GetCache() override;
    HttpNetworkSession* GetSession() override;

    base::WeakPtr<HttpCache> GetWeakPtr() { return weak_factory_.GetWeakPtr(); }

    // Resets the network layer to allow for tests that probe
    // network changes (e.g. host unreachable).  The old network layer is
    // returned to allow for filter patterns that only intercept
    // some creation requests.  Note ownership exchange.
    std::unique_ptr<HttpTransactionFactory>
    SetHttpNetworkTransactionFactoryForTesting(
        std::unique_ptr<HttpTransactionFactory> new_network_layer);

private:
    // Types --------------------------------------------------------------------

    // Disk cache entry data indices.
    enum {
        kResponseInfoIndex = 0,
        kResponseContentIndex,
        kMetadataIndex,

        // Must remain at the end of the enum.
        kNumCacheEntryDataIndices
    };

    class MetadataWriter;
    class QuicServerInfoFactoryAdaptor;
    class Transaction;
    class WorkItem;
    friend class Transaction;
    friend class ViewCacheHelper;
    struct PendingOp; // Info for an entry under construction.

    typedef std::list<Transaction*> TransactionList;
    typedef std::list<WorkItem*> WorkItemList;

    struct ActiveEntry {
        explicit ActiveEntry(disk_cache::Entry* entry);
        ~ActiveEntry();

        disk_cache::Entry* disk_entry;
        Transaction* writer;
        TransactionList readers;
        TransactionList pending_queue;
        bool will_process_pending_queue;
        bool doomed;
    };

    using ActiveEntriesMap = std::unordered_map<std::string, ActiveEntry*>;
    using PendingOpsMap = std::unordered_map<std::string, PendingOp*>;
    using ActiveEntriesSet = std::set<ActiveEntry*>;
    using PlaybackCacheMap = std::unordered_map<std::string, int>;

    // Methods ------------------------------------------------------------------

    // Creates the |backend| object and notifies the |callback| when the operation
    // completes. Returns an error code.
    int CreateBackend(disk_cache::Backend** backend,
        const CompletionCallback& callback);

    // Makes sure that the backend creation is complete before allowing the
    // provided transaction to use the object. Returns an error code.  |trans|
    // will be notified via its IO callback if this method returns ERR_IO_PENDING.
    // The transaction is free to use the backend directly at any time after
    // receiving the notification.
    int GetBackendForTransaction(Transaction* trans);

    // Generates the cache key for this request.
    std::string GenerateCacheKey(const HttpRequestInfo*);

    // Dooms the entry selected by |key|, if it is currently in the list of active
    // entries.
    void DoomActiveEntry(const std::string& key);

    // Dooms the entry selected by |key|. |trans| will be notified via its IO
    // callback if this method returns ERR_IO_PENDING. The entry can be
    // currently in use or not.
    int DoomEntry(const std::string& key, Transaction* trans);

    // Dooms the entry selected by |key|. |trans| will be notified via its IO
    // callback if this method returns ERR_IO_PENDING. The entry should not
    // be currently in use.
    int AsyncDoomEntry(const std::string& key, Transaction* trans);

    // Dooms the entry associated with a GET for a given |url|.
    void DoomMainEntryForUrl(const GURL& url);

    // Closes a previously doomed entry.
    void FinalizeDoomedEntry(ActiveEntry* entry);

    // Returns an entry that is currently in use and not doomed, or NULL.
    ActiveEntry* FindActiveEntry(const std::string& key);

    // Creates a new ActiveEntry and starts tracking it. |disk_entry| is the disk
    // cache entry.
    ActiveEntry* ActivateEntry(disk_cache::Entry* disk_entry);

    // Deletes an ActiveEntry.
    void DeactivateEntry(ActiveEntry* entry);

    // Deletes an ActiveEntry using an exhaustive search.
    void SlowDeactivateEntry(ActiveEntry* entry);

    // Returns the PendingOp for the desired |key|. If an entry is not under
    // construction already, a new PendingOp structure is created.
    PendingOp* GetPendingOp(const std::string& key);

    // Deletes a PendingOp.
    void DeletePendingOp(PendingOp* pending_op);

    // Opens the disk cache entry associated with |key|, returning an ActiveEntry
    // in |*entry|. |trans| will be notified via its IO callback if this method
    // returns ERR_IO_PENDING.
    int OpenEntry(const std::string& key, ActiveEntry** entry,
        Transaction* trans);

    // Creates the disk cache entry associated with |key|, returning an
    // ActiveEntry in |*entry|. |trans| will be notified via its IO callback if
    // this method returns ERR_IO_PENDING.
    int CreateEntry(const std::string& key, ActiveEntry** entry,
        Transaction* trans);

    // Destroys an ActiveEntry (active or doomed).
    void DestroyEntry(ActiveEntry* entry);

    // Adds a transaction to an ActiveEntry. If this method returns ERR_IO_PENDING
    // the transaction will be notified about completion via its IO callback. This
    // method returns ERR_CACHE_RACE to signal the transaction that it cannot be
    // added to the provided entry, and it should retry the process with another
    // one (in this case, the entry is no longer valid).
    int AddTransactionToEntry(ActiveEntry* entry, Transaction* trans);

    // Called when the transaction has finished working with this entry. |cancel|
    // is true if the operation was cancelled by the caller instead of running
    // to completion.
    void DoneWithEntry(ActiveEntry* entry, Transaction* trans, bool cancel);

    // Called when the transaction has finished writing to this entry. |success|
    // is false if the cache entry should be deleted.
    void DoneWritingToEntry(ActiveEntry* entry, bool success);

    // Called when the transaction has finished reading from this entry.
    void DoneReadingFromEntry(ActiveEntry* entry, Transaction* trans);

    // Converts the active writer transaction to a reader so that other
    // transactions can start reading from this entry.
    void ConvertWriterToReader(ActiveEntry* entry);

    // Returns the LoadState of the provided pending transaction.
    LoadState GetLoadStateForPendingTransaction(const Transaction* trans);

    // Removes the transaction |trans|, from the pending list of an entry
    // (PendingOp, active or doomed entry).
    void RemovePendingTransaction(Transaction* trans);

    // Removes the transaction |trans|, from the pending list of |entry|.
    bool RemovePendingTransactionFromEntry(ActiveEntry* entry,
        Transaction* trans);

    // Removes the transaction |trans|, from the pending list of |pending_op|.
    bool RemovePendingTransactionFromPendingOp(PendingOp* pending_op,
        Transaction* trans);
    // Resumes processing the pending list of |entry|.
    void ProcessPendingQueue(ActiveEntry* entry);

    // Events (called via PostTask) ---------------------------------------------

    void OnProcessPendingQueue(ActiveEntry* entry);

    // Callbacks ----------------------------------------------------------------

    // Processes BackendCallback notifications.
    void OnIOComplete(int result, PendingOp* entry);

    // Helper to conditionally delete |pending_op| if the HttpCache object it
    // is meant for has been deleted.
    //
    // TODO(ajwong): The PendingOp lifetime management is very tricky.  It might
    // be possible to simplify it using either base::Owned() or base::Passed()
    // with the callback.
    static void OnPendingOpComplete(const base::WeakPtr<HttpCache>& cache,
        PendingOp* pending_op,
        int result);

    // Processes the backend creation notification.
    void OnBackendCreated(int result, PendingOp* pending_op);

    // Variables ----------------------------------------------------------------

    NetLog* net_log_;

    // Used when lazily constructing the disk_cache_.
    std::unique_ptr<BackendFactory> backend_factory_;
    bool building_backend_;
    bool bypass_lock_for_test_;
    bool fail_conditionalization_for_test_;

    Mode mode_;

    std::unique_ptr<HttpTransactionFactory> network_layer_;

    std::unique_ptr<disk_cache::Backend> disk_cache_;

    // The set of active entries indexed by cache key.
    ActiveEntriesMap active_entries_;

    // The set of doomed entries.
    ActiveEntriesSet doomed_entries_;

    // The set of entries "under construction".
    PendingOpsMap pending_ops_;

    std::unique_ptr<PlaybackCacheMap> playback_cache_map_;

    // A clock that can be swapped out for testing.
    std::unique_ptr<base::Clock> clock_;

    base::WeakPtrFactory<HttpCache> weak_factory_;

    DISALLOW_COPY_AND_ASSIGN(HttpCache);
};

} // namespace net

#endif // NET_HTTP_HTTP_CACHE_H_
